1. Field of the Invention
The present invention relates to a chiral tetraaminophosphonium salt, a catalyst for asymmetric synthesis comprising this chiral tetraaminophosphonium salt or conjugated base thereof, and a method for producing chiral β-nitroalcohols using this chiral tetraaminophosphonium salt or conjugated base thereof.
2. Related Art
β-nitroalcohols are widely used as synthesis intermediates for biologically active substances such as drugs and agricultural chemicals, and as raw materials for the synthesis of fine chemicals. The nitroaldol reaction (Henry reaction) involving a reaction between a nitroalkane and an aldehyde is a known method for synthesizing the β-nitroalcohol.
There is currently a desire for the development of methods for obtaining compounds having specific steric structures rather than unspecified target compounds, specifically, synthesis reactions that are stereoselective. For example, there are many chiral isomers having asymmetric carbon atoms in biologically active substances. Therefore, it is important to obtain chiral isomers having the desired absolute configuration. An example of the method for the production of chiral isomers is a method including synthesizing a racemic mixture and separating chiral isomers by optical resolution or the like. However, such methods have poor efficiency due to the requirement of chemical conversion and so on. Thus, developments also have been advancing in regard to asymmetric synthesis methods for selectively obtaining chiral isomers of β-nitroalcohols.
“Eur. J. Org. Chem. (2007) 2561-2574” describes the stereoselective synthesis of β-nitroalcohol by nitroaldol reaction using various catalysts.
JP-A-2005-272339 describes the methods for the production of chiral β-nitroalcohols by nitroaldol reaction in the presence of a chiral metal complex catalyst having cobalt ion or chromium ion.
JP-A-2006-36737 describes the methods for the production of chiral β-nitroalcohols by reacting an aromatic aldehyde and nitromethane in the presence of copper catalyst, and a copper compound and a chiral bisoxazoline compound or chiral diamine having a specific structure are allowed to come into contact to obtain a copper catalyst.
However, with methods for producing β-nitroalcohols by conventional nitroaldol reactions, the structures of the aldehydes and nitroalkanes that can be used are limited. In addition, there is currently a desire for the development of methods for producing β-nitroalcohols that have superior yields and stereoselectivity.